In a solid-state component, the electric current is confined to solid elements and compounds engineered specifically to switch and amplify it. Current flow can be understood in two forms: as negatively charged electrons, and as positively charged electron deficiencies called holes.

The first solid-state device was the "cat's whisker" detector, first used in 1906 radio receiver.[7] A whisker-like wire is placed lightly in contact with a solid crystal (such as a germanium crystal) in order to detect a radio signal by the contact junction effect.[8] The solid-state device came into its own with the invention of the transistor in 1947.